1. Technical Field
The disclosure relates to a master/slave decision device applied to a network device.
2. Description of the Prior Art
In the High-Definition Multimedia Interface (HDMI) standard version 1.4, a fast Ethernet standard is adopted to transmit data having the data rate equal to 100 Mbps. In the conventional fast Ethernet standard, a transmission signal and a receiving signal of a network device are transmitted on different channels. Therefore, the transmission signal will not bounce back and cause echo. However, in the HDMI Ethernet & Audio Return Channel (HEAC), the receiver requires an additional echo canceller to cancel the transmission signal from its own to prevent from interfered by its transmission signal because the transmission signal and the receiving signal are transmitted on a single pair of transmission line and the echoes are caused thereby.
However, when both a network device and another network device send out the same signal at the same time, the receiving end of the network device is unable to distinguish whether the received signal is from the other network device or the echo signal caused by the transmission signal. If the received signal is from the other network device, the network device should receive this signal; and if the received signal is caused by the transmission signal, the received signal should be cancelled. For example, FIG. 1 is a diagram illustrating a scrambler 100 applied in fast Ethernet. The scrambler 100 includes eleven registers D1-D11 and two adders 102 and 104, where the values of the registers D1-D11 serve as a seed. When both the network device and the other network device do not send out packets, a source stream DS will be a series of “1”, at this time when seeds of their scramblers are the same, the transmission signals TS of both the network device and the other network device will also be the same. It is noted that, because of the signal delay on the transmission line and inter-symbol interference (ISI), the interference happens when the seed distance between the scramblers of the network device and the other network device is not large enough. In addition, because the local clocks of the network device and the other network device may be slightly different, the seed overlap issue may be occurred over time.